2D Modelica modelling and experimental validation of a compact cross-flow heat exchanger used in a new desiccant evaporative cooling system

Building electrification presents a significant challenge for the power grid, in part given the increase in cooling demand due to global warming. Thermally activated Desiccant Evaporative Cooling (DEC) systems can be an alternative used for cooling, dehumidification, ventilation and heating. They can help reduce the electrical load of air conditioning systems, especially if connected to existing district heating networks. FREESCOO 3.0 is a DEC system designed to work with regeneration temperatures as low as 60 (Formula presented.) C, making it compatible with the operating conditions of 4th generation district heating. This device has been developed and tested in an accredited laboratory, in order to be tested subsequently on the field in a residential building located in Milan (Italy). The core component of the system is a compact air-to-air heat exchanger packed with silica gel grains as adsorption beds, which allows simultaneous dehumidification and cooling of the process air. The overall effectiveness, efficiency, and economy of the system depends on the performance and cost of the heat exchanger. However, traditional static design approaches fall short since by definition FREESCOO operation is transient. Therefore, an experimental bed was designed to recreate the operating conditions that will be encountered in the real installation. Milan indoor and weather conditions for air temperature and humidity were emulated using two climatic chambers, and a water loop operating at 60 (Formula presented.) C for the DEC regeneration. The resulting 100 experimental data points at different temperature, humidity and airflow rate were used to validate a new open source Modelica library modelling the different components of the heat exchanger. The 2D finite volume model of the new heat exchanger shows an error of less than 6% Normalized Root Mean Square Error (NRMSE) on water and energy balances in the validation cycles.